1. Field of the Invention
This invention pertains to the use of spectral gamut mapping, and in particular, pertains to spectral gamut mapping based on a colorimetric gamut mapping.
2. Related Background Art
There is an increasing trend for color imaging applications to process and utilize spectral data, and/or to perform color processing in a spectral color space. For example, it has become common to characterize color devices such as scanners, cameras, printers and displays, in terms of their spectral responsively, such as by obtaining a so-called spectral device profile. Once a spectral characterization of a device is obtained, operations such as transforming color data from a source device to a destination device, gamut mapping, etc., can be performed in the full spectral space.
As another example, some modem image capture devices can capture color image data in spectral or extended color spaces. In this regard, the use of spectral data such as spectral reflectance of objects and spectral power distribution of illuminants promises to yield even more advantages in the near future. Ultimately, one goal of spectral color reproduction is to produce color reproductions with remarkably high color fidelity, perhaps even matching the original scene on the spectral level. In the case of reflective objects, for example, a reproduction with a spectral match would have the same color as the original object under any illuminant.
Spectral characterization of color devices, and development of multi-spectral devices such as multi-spectral cameras and multi-spectral printers, could form the basis of a spectral color management workflow that can have very useful applications in everyday consumer products. For example, such technologies could allow online shoppers to print their own “virtual swatches” of fabrics, as detailed in the paper “Answering Hunt's Web Shopping Challenge: Spectral Color Management for a Virtual Swatch” by Rosen et al., Proceedings of the IS&T/SID 9th Color Imaging Conference, pp. 267-272. Another application of spectral color management in computer aided design/computer aided manufacturing (CAD/CAM) applications allows manufacturers to visualize and demonstrate preliminary design ideas by simulation, before actually building a costly prototype.
While the use of spectral data can provide many advantages, such as reducing metamerism, using spectral data presents some challenges in the context of gamut mapping. As in the calorimetric case where different devices have different colorimetric gamuts, in the spectral case, different devices have different spectral gamuts. Spectral color reproduction requires accommodating the difference in spectral gamuts. A standard approach to this problem in the calorimetric case is gamut mapping. Extending conventional, calorimetric gamut mapping algorithms to spectral gamut mapping algorithms however requires overcoming some difficulties. In particular, unlike conventional color spaces such as CIELAB and CIECAM02, there is no appearance attributes such as lightness or chroma to establish mapping direction. A basic question for spectral gamut mapping is how to design algorithms that do not require these appearance attributes.
Another difficulty comes from the high dimensionality of the spectral data. A known approach to this problem is the construction of Interim Connection Spaces (ICSs), which are of lower dimension than the full spectral space. Gamut mapping in ICSs instead of the full spectral space can alleviate some of the computational burden associated with high dimension, but the problem is still formidable without novel algorithms. This is because, although the dimension of the ICS is lower, it is nevertheless higher than three dimensions. Consequently, use of ICS in computationally intensive operations such as certain geometrical operations used in gamut mapping can be a major bottleneck in a spectral color management computational pipeline.